Characteristics and runoff volume of the Yangtze River paleo-valley at Nanjing reach in the Last Glacial Maximum

Abstract

The stratigraphical cross-sections of the Yangtze River incised-valley near the No.1, No.3 and No.4 Nanjing Yangtze River bridges were established with respective bore date and documents. By ¹⁴C age analysis of the samples of four drilling cores near the No.4 Bridge (to be built), we can find that the time range of paleo-valley is dated in the LGM at a depth of −60 m to −90 m near Nanjing. It is also indicated that the deep incised-valley channel was narrow and the river flowed swiftly. The ancient Yangtze River deep channel presented partially and deeply incised features near the No.1 Bridge. According to previous publications, much research has been done on the main paleo-channel of the Yangtze River, but few results have been achieved on discharge estimation. In this paper, the incipient velocity and average velocity of the LGM was calculated with $V_c = 4.60d^{{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}} h^{{1 \mathord{\left/ {\vphantom {1 6}} \right. \kern-\nulldelimiterspace} 6}} ,V_c = 1.281g\left( {13.15.\frac{h} {{d_{95} }}} \right)\sqrt {gd} ,V \approx 6.5u_* \left| {\frac{h} {{d_{90} }}} \right|^{\tfrac{1} {6}}$, etc., in terms of the river shape, sedimentary grain size and sequences near the No.3 and No.1 bridges. Moreover, the discharge in Nanjing reach of the Yangtze River during the LGM has been estimated to be around 12,000–16,000 m³/s according to the relationship of discharge, velocity of flow and cross-section.